Biology Reference
In-Depth Information
11 8
LIFE HISTORY
The winter is passed in the egg stage on blackthorn
(
Prunus spinosa
) and various other species of
Prunus
,
the primary hosts. Eggs hatch in the following spring
and small colonies then develop on the shoots. Winged
forms are produced in the early summer and these
migrate to various aquatic plants, including arrow-head
(
Sagittaria sagittifolia
), false bulrush (
Typha latifolia
)
and water-plantain (
Alisma plantago-aquatica
); large
colonies often develop on water-lilies, the aphids
congregating along the leaf veins and also invading the
flowers. In the autumn, there is a return migration to
primary hosts, where sexual reproduction occurs and
eggs are laid.
11 8
Colony of banana aphid (
Pentalonia nigronervosa
).
DAMAGE
Primary hosts:
if attacks are heavy, young leaves at the
tips of the new shoots become crinkled.
Secondary
hosts:
heavy infestations cause considerable distortion
of the stems and foliage, and also discolour the flowers.
11 9
Rhopalosiphum insertum
(Walker) (
120
)
syn.
R. crataegellum
(Theobald)
Apple/grass aphid
Minor infestations of this generally common species
sometimes occur on crab-apple (
Malus
),
Cotoneaster
,
hawthorn (
Crataegus
), Japanese quince (
Chaenomeles
japonica
), medlar (
Mespilus germanica
), rowan (
Sorbus
aucuparia
) and other species of
Sorbus
, causing leaf
distortion. The aphids overwinter as eggs on rosaceous
primary hosts, with colonies developing on the shoots in
the following spring. Eventually, winged forms are
produced and these migrate to the roots of grasses, the
secondary hosts. A return migration to primary hosts
occurs in the autumn. Apterae (2.1-2.6 mm long) are
yellowish green, with darker longitudinal stripes down
the body, short, dark-tipped antennae, and short, light
green, distinctly flanged siphunculi. Attacks on
ornamentals are usually insignificant but may be of
some importance on young plants, including nursery
stock.
11 9
Colony of water-lily aphid (
Rhopalosiphum nymphaeae
).
120
120
Apple/grass aphid (
Rhopalosiphum insertum
) damage to
leaves of
Sorbus sargentiana
.
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